Such a method is used to interpolate analog signals generated by scanning a measuring graduation, for position-measuring, i.e., especially for measurement of lengths and/or angles. In this connection, the analog signals are respectively converted into a digital data stream, with the aid of a sigma-delta modulator. For generating a (single) string of results, the at least two data streams are then first combined with correctional factors and subsequently with one another. From the string of results, on the one hand, new correctional values are generated in the light of the quality criterion to be satisfied (by the values of the string of results), and on the other hand, the output signals of the interpolation are generated.
The at least two analog signals are particularly phase-shifted by 90° to one another, and are essentially sinusoidal, the latter also including analog signals generated from the sine function by phase-shifting, such as cosine signals.
Such a method is described in German Published Patent Application No. 199 38 802. In this method, the string of results is supplied to a digital filter, which restores certain data of the input signals, and which subsequently increments or decrements a phase counter as a function of the output value of the filter. The phase value generated hereby is used on the one hand (up to the fulfillment of the quality criterion) for determining new correctional values, and on the other hand for determining the output signal of the interpolation. For the satisfaction of the quality criterion, the string of results generates a signal sequence or string in a filter, at simultaneous decimation, which, after comparison to the quality criterion, controls the correctional values such that the string of results approaches this quality criterion, and in addition, a string of addresses is formed from which, after low-pass filtering and association, the output signals are generated.
German Published Patent Application No. 195 02 276 describes an interpolation method for interpolating at least two sine-like analog signals, for measuring paths and/or angles, that are obtained by the scanning of a graduation carrier, are position-dependent, periodic and phase-shifted by 90° to one another, in which noise is superimposed on the analog signals in each case using sigma-delta modulation, in which, from the thus generated data strings, upon simultaneous first incomplete low-pass filtering of the noise components above the maximum input frequency of the analog signals, sequences of signals are generated, and in which, from the sequences of signals, a sequence of angular values is obtained to which is assigned, after a second low-pass filtering of the still-present noise component, above the maximum input frequency of the analog signals, a string of output values.
German Published Patent Application No. 195 06 276 describes a method for interpolating sensor signals, in which respectively one sine signal and one cosine signal of a sensor is supplied to a bridge circuit having several tapping points and a value comparison is carried out between a tapping pair, made up of two tapping points which are diametrically opposite in the bridge circuit. If a value equality between the tapping pair is determined which corresponds to a zero crossing of the scanning value, a signal representing the setting of the corresponding tapping pair is emitted. In this context, the tapping pairs are scanned one after another in one direction, are subjected, one after another, to the value comparison, and a count value is assigned to each scanning event. Appropriate to the result of the comparison, a phase counter is incremented or decremented.